How to Source Castings
Casting RFQ checklist: cast alloy spec, process, as-cast and machined models, draft, tolerances, soundness and NDT, tooling ownership and first article.
514 metal casting companies in the Noramark directory
Buying a casting means buying two things: the tooling (a pattern and core boxes, a wax injection die, or a die-casting die) and the parts poured from it. Tooling is a one-time cost that runs from a few thousand dollars for a simple pattern to tens of thousands or more for a die-casting die, and the process you pick decides how precise, how sound and how cheap each part will be. Sand, investment and die casting overlap less than people assume.
A good casting RFQ gives the alloy by its casting spec, the as-cast and machined geometry, the tolerances and finish expected as cast, the soundness requirements and how they are tested, and the annual volume that justifies the tooling. It also settles who owns the tooling and who machines the casting: a foundry that also machines can hold the relationship between cast and machined surfaces better than two vendors blaming each other.
RFQ checklist
15 things to settle on the drawing or in the request before you ask for casting quotes. Print it and tick it off against the print, or copy it into the RFQ.
Alloy and process
Alloy by casting designation and spec, not a wrought grade: for example A356-T6 or A380 aluminum, ASTM A48 Class 30 gray iron, ASTM A536 65-45-12 ductile iron, CF8M (cast 316) or CB7Cu-1 (cast 17-4 PH)
Cast alloys have their own designations and properties. Asking for a "6061 casting" or a "316 casting" gets a phone call or a substitution you did not approve.
Casting process, or the tolerance, finish and volume that let the foundry recommend one: sand, investment, permanent mold or die casting
Process sets tooling cost, tolerances, minimum wall and surface finish. If you are unsure, give the requirements and ask for a recommendation.
Heat treatment and required mechanical properties, and how they are proven: separately cast test bars, attached coupons, or specimens cut from a casting
Casting properties vary with section size and heat treatment, and the three kinds of test specimen give different numbers.
Geometry and tolerances
An as-cast model and a machined model, or one model with machining stock shown
The foundry builds tooling from the as-cast shape; the machinist works to the finished part. One model for both leaves draft and stock to guesswork.
Draft, minimum wall thickness, and parting line location if it matters
Surfaces pulled from a mold need draft, commonly 1-3 degrees in sand and much less in investment casting. The foundry will add it where it is missing, which may move surfaces you care about.
Casting tolerances by standard (ISO 8062-3 grade, or the foundry's published standard), with critical dimensions marked
As-cast tolerances grow with size and vary by process: sand castings commonly hold about ±0.8-1.5 mm (±1/32-1/16") on moderate dimensions, investment castings about ±0.13 mm per 25 mm (±0.005" per inch).
Datum targets on cast surfaces for the first machining operation
Datum targets let the foundry check the casting and the machinist fixture it the same way. Without them, a casting that measures good can still machine bad.
As-cast surface finish, and cosmetic or sealing zones
Sand castings run roughly 6-25 µm Ra (250-1000 µin) and investment castings about 1.6-3.2 µm (63-125 µin). Name the surfaces that are visible or must seal.
Soundness and repair
Soundness by zone: allowable porosity and inclusions, radiographic grade against reference radiographs (for example ASTM E446 for steel, E155 for aluminum), magnetic particle or penetrant, and leak testing for fluid parts
NDT is priced per part and per method. Naming the zones and levels that matter keeps the whole casting from being held to the worst-case standard.
Vacuum impregnation allowed or not, for sealing porosity
Impregnation seals micro-porosity in die castings and some sand castings; some applications forbid it.
Weld repair allowed or not, and with what approval and documentation
Weld repair of defects is normal foundry practice for many alloys. Forbidding it raises the scrap rate and the price, so decide before the quote.
Tooling, approval and delivery
Tooling ownership, storage, maintenance and expected tooling life
Customer-owned tooling can move to another foundry; foundry-owned tooling cannot. Die-casting dies wear out after a number of shots that depends on alloy and design.
Sample castings and first article: layout inspection, material certs with chemistry and properties per heat, and approval before production
The first castings off new tooling nearly always need a tooling adjustment. Plan the time and cost for samples and a second iteration.
Who machines the casting, and whether it ships raw, machined, primed or painted
A foundry that machines owns the whole result. Split sourcing works, but the datum targets and the stock allowance must be agreed by both vendors.
Annual volume, order quantity and release pattern
Foundries pour by melt and pattern setup, so frequent small releases cost more per part than fewer larger ones, and volume decides the process and the tooling.
What to send with the RFQ
- As-cast and machined STEP models, or one model with stock shown.
- A drawing with alloy spec, casting tolerances, datum targets, soundness requirements and machined features.
- Annual volume and order quantity, which decide the process and the tooling.
- Details of existing tooling, if you are moving a part from another foundry.
- What the part does (pressure, load, wear, appearance), so the foundry can suggest alloy or process changes.
Lead times
| Prototype or first parts | Sand castings from a new pattern: about 4-8 weeks to first samples. Investment castings: 6-10 weeks with a new wax die, or 2-4 weeks from 3D-printed patterns. For one or two parts, machining from solid is often faster. |
|---|---|
| Production or repeat orders | Die-casting dies: roughly 10-16 weeks to build and sample. Repeat production from existing tooling: 3-8 weeks depending on the foundry schedule and machining. |
Typical of U.S. job shops, from order or approved drawing to shipment; confirm with the shop for your part.
What drives the cost
- Tooling: patterns and core boxes for sand, wax dies for investment, hardened steel dies for die casting.
- Cores: every internal passage adds a core box, core making and handling.
- Alloy: stainless, nickel alloys and bronzes cost several times iron or aluminum per pound.
- Part weight and yield, meaning how much metal goes to gates and risers.
- Soundness and NDT requirements that raise scrap and inspection cost.
- Machining stock and the number of machined features.
- Heat treatment, impregnation and finishing.
Common mistakes
- Calling out a wrought alloy (6061, 304) for a cast part.
- Sending only the machined model, so the foundry has to invent draft and stock.
- Holding as-cast surfaces to machining tolerances.
- No datum targets, so the foundry and the machinist measure the casting differently.
- Radiographic requirements over the whole casting when only a few zones carry load or pressure.
- Paying for tooling before settling who owns it.
Questions to ask the shop
- Which process do you recommend for this volume and tolerance, and why?
- Do you build tooling in-house, and who owns it once it is paid for?
- Do you machine castings in-house or through a partner?
- What NDT do you do in-house: X-ray, magnetic particle, penetrant, leak test?
- Is weld repair part of your normal practice for this alloy?
- What samples and inspection do you provide before production approval?
Typical processes
Typical materials
Charts and calculators
Frequently asked questions
- Sand casting, investment casting or die casting?
- Sand casting has the cheapest tooling and suits large parts and low volumes in iron, steel, aluminum and bronze, with coarse tolerances and finish. Investment casting makes precise, detailed parts in almost any alloy, including stainless and nickel alloys, at a higher part price. Die casting is for aluminum, zinc and magnesium at thousands of parts a year and up, where an expensive die buys a low part price and fine detail.
- When is a casting cheaper than machining from solid?
- When the tooling cost spreads over enough parts, or when machining would turn most of the bar or plate into chips. The break-even is often somewhere between tens and hundreds of parts a year for sand and investment castings, and thousands for die castings. A foundry and a machine shop can each price both routes if you ask.
- What does draft mean on a casting?
- Draft is a taper on surfaces parallel to the direction the pattern or die is pulled, so the part releases without tearing the mold. Sand castings commonly need 1-3 degrees, die castings roughly 0.5-2 degrees depending on wall and alloy, and investment castings little or none. Draw it or let the foundry add it, but say which surfaces it may not touch.
Build the RFQ: attach the print and this checklist
Attach the drawing (PDF) and the model (STEP), and put your answers to the checklist in the description. A Noramark sourcing specialist matches the request with U.S. shops that make castings and contacts you within 1 business day.
